Alexandrite

Chrysoberyl comes in a few different unique varieties, including the chameleon-like alexandrite. In natural or fluorescent light, it can appear a gorgeous shade of green, but in the warm, fluorescent lighting of a lamp or candle flame, it can turn brownish or purple red. This is a result of the mineral's complicated method of light absorption.

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Alexandrite’s dramatic color change is sometimes described as “emerald by day, ruby by night.” Other gems also change color in response to a light-source change, but this gem’s transformation is so striking that the phenomenon itself is often called “the alexandrite effect.”